The present invention relates to closures for containers.
In EP-A-0408364, there is described a container closure molded from plastics material and comprising a crown, an annular skirt depending from the crown and formed with a screw thread on its internal surface, and a tamper evident ring connected to the end of the skirt remote from the crown by a series of frangible bridges extending across an axial gap between the ring and the skirt, or by a band of the material with a circumferential line of weakening therein. The ring has spaced along its inner surface a plurality of radially inwardly projecting protrusions each having an abutment surface a plurality of radially inwardly projecting protrusions each having an abutment surface generally facing the crown but having a slight inclination away from the crown in the radially inward direction, and an inwardly facing cam surface inclined away from the crown. Whereas this arrangement works satisfactorily there are improvements which can be made to improve its performance.
One of the problems with arrangements of the above type is that in order to provide an adequate abutment surface for contact with the shoulder of security band formed on the neck of the container to which the closure is to be applied, regularly spaced double-ended protrusions are provided at regular intervals about a ring. The effect of this is to reduce the extensibility of the ring because the relative lengths of the protrusions have the side effect of reducing the flexibility and extensibility of the ring. The effect is to require a relatively high torque setting on the capping machine, during assembly with a container neck, in order to force the ring over the security band on the neck of the container during the capping procedure. Because the torque setting of the capping machine has to be high, a further side effect is that the closure is driven onto the container neck by the capping machine such that unscrewing can require significant strength. Further, because of the lack of extensibility there is a certain failure rate among the closures and the capping rate is reduced.